kernel/time/timekeeping.c

/*
 *  linux/kernel/time/timekeeping.c
 *
 *  Kernel timekeeping code and accessor functions
 *
 *  This code was moved from linux/kernel/timer.c.
 *  Please see that file for copyright and history logs.
 *
 */

#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/sysdev.h>
#include <linux/clocksource.h>
#include <linux/jiffies.h>
#include <linux/time.h>
#include <linux/tick.h>


/*
 * This read-write spinlock protects us from races in SMP while
 * playing with xtime and avenrun.
 */
__attribute__((weak)) __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);

EXPORT_SYMBOL(xtime_lock);


/*
 * The current time
 * wall_to_monotonic is what we need to add to xtime (or xtime corrected
 * for sub jiffie times) to get to monotonic time.  Monotonic is pegged
 * at zero at system boot time, so wall_to_monotonic will be negative,
 * however, we will ALWAYS keep the tv_nsec part positive so we can use
 * the usual normalization.
 */
struct timespec xtime __attribute__ ((aligned (16)));
struct timespec wall_to_monotonic __attribute__ ((aligned (16)));

EXPORT_SYMBOL(xtime);


static struct clocksource *clock; /* pointer to current clocksource */


#ifdef CONFIG_GENERIC_TIME
/**
 * __get_nsec_offset - Returns nanoseconds since last call to periodic_hook
 *
 * private function, must hold xtime_lock lock when being
 * called. Returns the number of nanoseconds since the
 * last call to update_wall_time() (adjusted by NTP scaling)
 */
static inline s64 __get_nsec_offset(void)
{
	cycle_t cycle_now, cycle_delta;
	s64 ns_offset;

	/* read clocksource: */
	cycle_now = clocksource_read(clock);

	/* calculate the delta since the last update_wall_time: */
	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

	/* convert to nanoseconds: */
	ns_offset = cyc2ns(clock, cycle_delta);

	return ns_offset;
}

/**
 * __get_realtime_clock_ts - Returns the time of day in a timespec
 * @ts:		pointer to the timespec to be set
 *
 * Returns the time of day in a timespec. Used by
 * do_gettimeofday() and get_realtime_clock_ts().
 */
static inline void __get_realtime_clock_ts(struct timespec *ts)
{
	unsigned long seq;
	s64 nsecs;

	do {
		seq = read_seqbegin(&xtime_lock);

		*ts = xtime;
		nsecs = __get_nsec_offset();

	} while (read_seqretry(&xtime_lock, seq));

	timespec_add_ns(ts, nsecs);
}

/**
 * getnstimeofday - Returns the time of day in a timespec
 * @ts:		pointer to the timespec to be set
 *
 * Returns the time of day in a timespec.
 */
void getnstimeofday(struct timespec *ts)
{
	__get_realtime_clock_ts(ts);
}

EXPORT_SYMBOL(getnstimeofday);

/**
 * do_gettimeofday - Returns the time of day in a timeval
 * @tv:		pointer to the timeval to be set
 *
 * NOTE: Users should be converted to using get_realtime_clock_ts()
 */
void do_gettimeofday(struct timeval *tv)
{
	struct timespec now;

	__get_realtime_clock_ts(&now);
	tv->tv_sec = now.tv_sec;
	tv->tv_usec = now.tv_nsec/1000;
}

EXPORT_SYMBOL(do_gettimeofday);
/**
 * do_settimeofday - Sets the time of day
 * @tv:		pointer to the timespec variable containing the new time
 *
 * Sets the time of day to the new time and update NTP and notify hrtimers
 */
int do_settimeofday(struct timespec *tv)
{
	unsigned long flags;
	time_t wtm_sec, sec = tv->tv_sec;
	long wtm_nsec, nsec = tv->tv_nsec;

	if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
		return -EINVAL;

	write_seqlock_irqsave(&xtime_lock, flags);

	nsec -= __get_nsec_offset();

	wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
	wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);

	set_normalized_timespec(&xtime, sec, nsec);
	set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);

	clock->error = 0;
	ntp_clear();

	update_vsyscall(&xtime, clock);

	write_sequnlock_irqrestore(&xtime_lock, flags);

	/* signal hrtimers about time change */
	clock_was_set();

	return 0;
}

EXPORT_SYMBOL(do_settimeofday);

/**
 * change_clocksource - Swaps clocksources if a new one is available
 *
 * Accumulates current time interval and initializes new clocksource
 */
static void change_clocksource(void)
{
	struct clocksource *new;
	cycle_t now;
	u64 nsec;

	new = clocksource_get_next();

	if (clock == new)
		return;

	now = clocksource_read(new);
	nsec =  __get_nsec_offset();
	timespec_add_ns(&xtime, nsec);

	clock = new;
	clock->cycle_last = now;

	clock->error = 0;
	clock->xtime_nsec = 0;
	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);

	tick_clock_notify();

	printk(KERN_INFO "Time: %s clocksource has been installed.\n",
	       clock->name);
}
#else
static inline void change_clocksource(void) { }
#endif

/**
 * timekeeping_is_continuous - check to see if timekeeping is free running
 */
int timekeeping_is_continuous(void)
{
	unsigned long seq;
	int ret;

	do {
		seq = read_seqbegin(&xtime_lock);

		ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

	} while (read_seqretry(&xtime_lock, seq));

	return ret;
}

/**
 * read_persistent_clock -  Return time in seconds from the persistent clock.
 *
 * Weak dummy function for arches that do not yet support it.
 * Returns seconds from epoch using the battery backed persistent clock.
 * Returns zero if unsupported.
 *
 *  XXX - Do be sure to remove it once all arches implement it.
 */
unsigned long __attribute__((weak)) read_persistent_clock(void)
{
	return 0;
}

/*
 * timekeeping_init - Initializes the clocksource and common timekeeping values
 */
void __init timekeeping_init(void)
{
	unsigned long flags;
	unsigned long sec = read_persistent_clock();

	write_seqlock_irqsave(&xtime_lock, flags);

	ntp_clear();

	clock = clocksource_get_next();
	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
	clock->cycle_last = clocksource_read(clock);

	xtime.tv_sec = sec;
	xtime.tv_nsec = 0;
	set_normalized_timespec(&wall_to_monotonic,
		-xtime.tv_sec, -xtime.tv_nsec);

	write_sequnlock_irqrestore(&xtime_lock, flags);
}

/* flag for if timekeeping is suspended */
static int timekeeping_suspended;
/* time in seconds when suspend began */
static unsigned long timekeeping_suspend_time;

/**
 * timekeeping_resume - Resumes the generic timekeeping subsystem.
 * @dev:	unused
 *
 * This is for the generic clocksource timekeeping.
 * xtime/wall_to_monotonic/jiffies/etc are
 * still managed by arch specific suspend/resume code.
 */
static int timekeeping_resume(struct sys_device *dev)
{
	unsigned long flags;
	unsigned long now = read_persistent_clock();

	write_seqlock_irqsave(&xtime_lock, flags);

	if (now && (now > timekeeping_suspend_time)) {
		unsigned long sleep_length = now - timekeeping_suspend_time;

		xtime.tv_sec += sleep_length;
		wall_to_monotonic.tv_sec -= sleep_length;
	}
	/* re-base the last cycle value */
	clock->cycle_last = clocksource_read(clock);
	clock->error = 0;
	timekeeping_suspended = 0;
	write_sequnlock_irqrestore(&xtime_lock, flags);

	touch_softlockup_watchdog();

	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);

	/* Resume hrtimers */
	hres_timers_resume();

	return 0;
}

static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
{
	unsigned long flags;

	write_seqlock_irqsave(&xtime_lock, flags);
	timekeeping_suspended = 1;
	timekeeping_suspend_time = read_persistent_clock();
	write_sequnlock_irqrestore(&xtime_lock, flags);

	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);

	return 0;
}

/* sysfs resume/suspend bits for timekeeping */
static struct sysdev_class timekeeping_sysclass = {
	.resume		= timekeeping_resume,
	.suspend	= timekeeping_suspend,
	set_kset_name("timekeeping"),
};

static struct sys_device device_timer = {
	.id		= 0,
	.cls		= &timekeeping_sysclass,
};

static int __init timekeeping_init_device(void)
{
	int error = sysdev_class_register(&timekeeping_sysclass);
	if (!error)
		error = sysdev_register(&device_timer);
	return error;
}

device_initcall(timekeeping_init_device);

/*
 * If the error is already larger, we look ahead even further
 * to compensate for late or lost adjustments.
 */
static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
						 s64 *offset)
{
	s64 tick_error, i;
	u32 look_ahead, adj;
	s32 error2, mult;

	/*
	 * Use the current error value to determine how much to look ahead.
	 * The larger the error the slower we adjust for it to avoid problems
	 * with losing too many ticks, otherwise we would overadjust and
	 * produce an even larger error.  The smaller the adjustment the
	 * faster we try to adjust for it, as lost ticks can do less harm
	 * here.  This is tuned so that an error of about 1 msec is adusted
	 * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
	 */
	error2 = clock->error >> (TICK_LENGTH_SHIFT + 22 - 2 * SHIFT_HZ);
	error2 = abs(error2);
	for (look_ahead = 0; error2 > 0; look_ahead++)
		error2 >>= 2;

	/*
	 * Now calculate the error in (1 << look_ahead) ticks, but first
	 * remove the single look ahead already included in the error.
	 */
	tick_error = current_tick_length() >>
		(TICK_LENGTH_SHIFT - clock->shift + 1);
	tick_error -= clock->xtime_interval >> 1;
	error = ((error - tick_error) >> look_ahead) + tick_error;

	/* Finally calculate the adjustment shift value.  */
	i = *interval;
	mult = 1;
	if (error < 0) {
		error = -error;
		*interval = -*interval;
		*offset = -*offset;
		mult = -1;
	}
	for (adj = 0; error > i; adj++)
		error >>= 1;

	*interval <<= adj;
	*offset <<= adj;
	return mult << adj;
}

/*
 * Adjust the multiplier to reduce the error value,
 * this is optimized for the most common adjustments of -1,0,1,
 * for other values we can do a bit more work.
 */
static void clocksource_adjust(struct clocksource *clock, s64 offset)
{
	s64 error, interval = clock->cycle_interval;
	int adj;

	error = clock->error >> (TICK_LENGTH_SHIFT - clock->shift - 1);
	if (error > interval) {
		error >>= 2;
		if (likely(error <= interval))
			adj = 1;
		else
			adj = clocksource_bigadjust(error, &interval, &offset);
	} else if (error < -interval) {
		error >>= 2;
		if (likely(error >= -interval)) {
			adj = -1;
			interval = -interval;
			offset = -offset;
		} else
			adj = clocksource_bigadjust(error, &interval, &offset);
	} else
		return;

	clock->mult += adj;
	clock->xtime_interval += interval;
	clock->xtime_nsec -= offset;
	clock->error -= (interval - offset) <<
			(TICK_LENGTH_SHIFT - clock->shift);
}

/**
 * update_wall_time - Uses the current clocksource to increment the wall time
 *
 * Called from the timer interrupt, must hold a write on xtime_lock.
 */
void update_wall_time(void)
{
	cycle_t offset;

	/* Make sure we're fully resumed: */
	if (unlikely(timekeeping_suspended))
		return;

#ifdef CONFIG_GENERIC_TIME
	offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
#else
	offset = clock->cycle_interval;
#endif
	clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;

	/* normally this loop will run just once, however in the
	 * case of lost or late ticks, it will accumulate correctly.
	 */
	while (offset >= clock->cycle_interval) {
		/* accumulate one interval */
		clock->xtime_nsec += clock->xtime_interval;
		clock->cycle_last += clock->cycle_interval;
		offset -= clock->cycle_interval;

		if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
			clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
			xtime.tv_sec++;
			second_overflow();
		}

		/* interpolator bits */
		time_interpolator_update(clock->xtime_interval
						>> clock->shift);

		/* accumulate error between NTP and clock interval */
		clock->error += current_tick_length();
		clock->error -= clock->xtime_interval << (TICK_LENGTH_SHIFT - clock->shift);
	}

	/* correct the clock when NTP error is too big */
	clocksource_adjust(clock, offset);

	/* store full nanoseconds into xtime */
	xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
	clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;

	/* check to see if there is a new clocksource to use */
	change_clocksource();
	update_vsyscall(&xtime, clock);
}